After flying a low approach at Port Angeles (KCLM) on the north side of the Olympic Peninsula, I picked up my clearance back to Boeing Field (KBFI), which was in a south flow, using runway 14R and 14L.
ATC typically vectors IFR traffic from the north or northwest—from points such as the San Juan Islands and airports on the Olympic Peninsula—to join the localizer for 14R (in fact, ATC really wants you track the final approach course; the LOC is just the time-honored way of accomplishing that goal). Often the clearance comes when you’re 30 to 40 miles from the airport, well outside the 18 nm standard range for a localizer.
When I receive such a clearance, I use a technique, demonstrated in this video, that’s available in most GPS navigators (for more information, see Setting a Course v. Vectors to Final).
A November 2022 update to the AIM includes a note in paragraph 1-1-9 Instrument Landing System, explaining that:
Unreliable signals may be received outside of these areas. ATC may clear aircraft on procedures beyond the service volume when the controller initiates the action or when the pilot requests, and radar monitoring is provided…All charted procedures with localizer coverage beyond the 18 NM SSV have been through the approval process for Expanded Service Volume (ESV) and have been validated by flight inspection.
A figure showing a chart for an ILS at Chicago O’Hare complements the note. It confirms that fixes along a localizer have been verified during the flight check process.
On the chart for the ILS to runway 14R at Boeing Field, however, the fix farthest out on the localizer is ISOGE, recently moved out to 12 nm from the runway, but still within the standard LOC service volume.
As the AIM notes, if ATC is monitoring you, controllers can direct you to join the LOC far from the airport, but such a clearance still leaves you with the problem of intercepting and tracking a course that may be wobbly—if it appears at all.
As the first part of the video shows, after loading the approach and transition, I select the appropriate course to an initial fix along the localizer, and I leave the CDI set to GPS. That setup, similar to using vectors-to-final, but preserving options if ATC changes the plan, draws a magenta reference line along the LOC that I can join and track inbound until I am close enough to receive a stable LOC signal, and then I switch the CDI to green needles.
When you are sure that you’re within the LOC service volume, change the CDI to LOC, and continue the approach with the approved lateral and vertical guidance for an ILS.
Because the weather was VMC when I flew the ILS for this video, I tested the technique and cross-checked what the LOC showed when I was far from the airport. The green needle was, to use a technical term, wonky, until I got close to ISOGE. My track would have been smoother and more accurate had I followed the magenta line until the LOC settled down near the initial fix.
BruceAir, LLC 
Since the LOC signal is ‘wonky’ as you say, why not stay GPS until near ISOGE. Use your same technique but stay GPS instead of VLOC until a quality signal? Confused.
As I explain in the video, since I was in basic VMC, I deliberately switched to the LOC early to observe its behavior compared to the GPS course.